Tight control of the activity of a therapeutic gene introduced in vivo is a major issue in gene therapy research. Appropriate levels of expression may be crucial for gene correction. The tetracycline-sensitive regulatory system is highly effective for transcriptional regulation of foreign genes in mammalian cells. Here we report tight tetracycline-dependent regulation of a luciferase reporter gene transferred into the rat brain in the genetically modified neural precursor cell line ST14A as early as 2 days and until at least 6 days after transplantation. This is the first demonstration of the potential of this regulatory system for the modulation of the expression of therapeutic genes introduced into the central nervous system.